Instead of referring to pin 13 in this program we assign a variable called blue.
This helps because:
1. it makes sense if a blue LED is connected to pin 13.
2. if you move the LED circuit to another pin in the Arduino you only have to change the pin ONCE.
Choose variable names that make sense to you and other humans. LED colors make sense. Buzzer is good. Servo makes sense. Cat doesn’t make as much sense unless you are programming a cat. Don’t use 21437843**$^&% as a variable name.
